Decorative molding techniques such as in-mold transfer, in-mold lamination and vacuum pressure molding lamination have been used for home electric appliances, auto interior parts and miscellaneous goods, and application ranges thereof are widely expanding due to the enhancement of environmental consciousness and the progress of technical innovation in recent years. Decorative molding films obtained by carrying out printing, shaping or metal deposition on a film are used for decorative molding. Acrylic films, PET films and polycarbonate films have been used as base films for these.
Characteristic properties required for the base films include thermoformability that ensures a target shape to be accurately transferred, solvent resistance required for the decoration of the surface of a film such as printing, surface hardness, heat resistance, transparency and weather resistance. However, there is no base material which satisfies all the above requirements, and the above films have been used according to purpose while they sustain problems.
For example, acrylic films are often used for decorative molding, making use of their excellent transparency and weather resistance. However, the acrylic films are unsatisfactory in terms of toughness and therefore readily crack or burr during molding, and there is limitation to the application of the films in fields which require high heat resistance. Although it is possible to improve the toughness of an acrylic resin to some extent by adding rubber particles to the acrylic resin to obtain a resin composition, transparency is often impaired in this case. Various studies have been made on the structure and production process of rubber particles to prevent a rise in haze even when the rubber particles are added. However, as satisfactory rubber particles are not found yet, it is difficult to satisfy the requirement for toughness and use acrylic films in fields which require high transparency.
In the case of polycarbonate films, although they have high heat resistance, they are inferior to acrylic films in thermoformability and it is therefore difficult to apply them in fields in which a complex shape or a deep shape is transferred accurately. Further, they have low surface hardness and solvent resistance.
Although PET films are superior to polycarbonate films in solvent resistance and surface hardness, they are biaxially oriented films and inferior to acrylic films and polycarbonate films which are unstretched films in stretchability. Therefore, they may be inferior in thermoformability. Further, they are inferior to these amorphous resins in transparency and have lower weather resistance than acrylic films.
As one of measures to improve the characteristic properties of the base material, there is proposed a multi-layer film having an acrylic resin layer on at least one side of a polycarbonate resin layer (Patent Documents 1 to 10).
This multi-layer film has improved toughness and heat resistance as compared with an acrylic film and improved surface hardness, solvent resistance and weather resistance as compared with a polycarbonate film. Thus, it is aimed to obtain good balance among properties by making use of the advantages of these films. However, the above multi-layer film is a laminate made of resins having different heat deformation temperatures, and its thermoformability and appearance and transparency after molding have often come into question.
Although various studies have been made to improve the characteristic properties of a base material for a decorative molding film from the viewpoints of the improvement of a raw material and the constitution of a laminate, the characteristic properties of the base material are not satisfactory yet and the further improvement of the properties is desired.    (Patent Document 1) Japanese Patent No. 3457514    (Patent Document 2) Japanese Patent No. 3489972    (Patent Document 3) Japanese Patent No. 3904262    (Patent Document 4) JP-A 2005-231257    (Patent Document 5) JP-A 2005-219330    (Patent Document 6) JP-A 2007-160892    (Patent Document 7) JP-A 2009-172953    (Patent Document 8) JP-A 2009-234183    (Patent Document 9) JP-A 2009-234184    (Patent Document 10) JP-A 2009-248363